Photoelectric consistency indicator for pulp



March 3, 1970 J. H. wm Emu. 3,498'Q71'9' PHOTOELECTRIC CONSISTENCY INDICATOR FOR PULP Filed Feb. 18, 1965 2 Sheets-Sheet 1 P10 HEHD BOX 14 16 72 cousmeucvr Z6 (CONSISTENCYOJZ) MEQSURM g cm.

V 36 so fij r 4o CONSISTENCY PouuER ,masum a mf 3'2 RECORDER SUPPLY mm? INVEMORS JAM as H. wme 59 --4 63 ROBERT HENLEY w 'l 3m5- March 3, 1970 J. H. wme ET AL I '3,498,7I "9 PHOTOELECTRIC CQNSISTENCY INDICATOR FOR PULP Filed Feb. 18, 1965 v 2 Sheets-Sheet 2 Ill-16.6

FOCAL POINT MEHSURNG CELL (PHOTO TUBE64 UGHT p p SOURC E 60 STOCK 92 98 TRNK 10o (coususweucv O- 570) 2 cousswsucv Minsumue CELL DiLU'HON WATER 106 INVENTORS JQQMES Hume 2 OBERT NBmLEY United States Patent 3,498,719 PHOTOELECTRIC CONSISTENCY INDICATOR FOR PULP James H. Wing and Robert N. Bailey, Augusta, Ga., as-

signors to Continental Can Company, linc., New York, N .Y., a corporation of New York Filed Feb. 18, 1965, Ser. No. 433,667 Int. Cl. G01n 1/00, 21/26 US. Cl. 35636 Claims ABSTRACT OF THE DISCLOSURE Methods and apparatus for determining the consistency of a non-homogeneous mixture, such as a pulp slurry, wherein radiant energy is projected through a flowing sample and the amount of energy transmitted through the sample is detected by a photo-detecting device. The sample of mixture is passed through a transparent tube constituting a lens having a given focal length and the photodetecting device is located at a point removed from the focal length to receive a low-resolution blurred image of the mixture sample in transit. A second photo-detecting device is directly illuminated and provides a reference for comparison with the response of the first-mentioned photodetecting device. Means for diluting the mixture sample at a controlled rate may be employed to alter the consistency of the sample to within a predetermined and relatively low optimum mixture consistency range of the disclosed apparatus.

This invention relates to a method and apparatus for determining the consistency of pulp and more specifically to a method and apparatus for projecting radiant energy, such as a light beam, through a flowing sample of the pulp slurry and detecting, such as by a photoelectric tube or the like, the amount of energy transmitted through the sample. The transmission quality of the sample, then manifested as an electrical output from the energy detector, can be correlated against known consistencies or concentrations to arrive at the consistency of the unknown sample.

In paper manufacturing processes, the consistency or percent of solids of the pulp slurry is a prime factor in the process. Different grades and weights of paper or paper products require different concentrations or consistencies of pulp. The pulp usually consists of the comminuted wood fibers, water, and the front-end additives.

The pulp is not a homogeneous mass but is a mixture which contains the foregoing materials and the pulp wood in the pulp appears as flocks. The flocks may contain varying amounts of pulp.

Since the consistency of the pulp is of prime importance in the manufacturing processes set forth, it is highly desirable and even mandatory that the consistency of the pulp be known at all times. Further, if truly successful operation is to be achieved, then the pulp consistency of unknown quantities must be easily ascertained and especially when the paper products system has been producing a particular grade of product and it is then desired to change to a different product, which may necessitate the employment of a pulp having a different consistency.

As the consistency of the pulp decreases, it becomes increasingly diflicult to accurately determine the true consistency of the pulp. The present invention is directed to an apparatus and method for determining the consistency of pulp in the range of 0% to 1.2% consistency. In addition, the determination is made instantly and continuously by observing the optical transmission qualities of the flowing pulp.

Other means are known for determining the consistency 3,498,719 Patented Mar. 3, 1970 of a pulp slurry. For example, a sample of the pulp may be weighed, dehydrated, and the remaining particles reweighed and by comparing the results of the second weighing with the first weighing, a percentage may be determined which is defined as the consistency of the pulp. Another method for determining the consistency of the pulp, may be through the employment of a viscometer; however, the accuracy of the results may be questionable due to the non-homogeneity of the sample. It will be intuitively clear that the foregoing methods of determining the consistency of the pulp suffer in many ways. For example, they are slow, ineflicient, and, in some instances, inaccurate. Accordingly, it becomes desirable to employ an apparatus and method for determining the consistency of pulp which is efficient, instantaneous, continuous, and, above all, with a high degree of accuracy. The present invention not only provides all the desirable qualities of the foregoing, but is also eflicient and accurate when employed in measuring and determining consistencies near 0% consistency.

Accordingly, it becomes the principal object of the present invention to improve methods and apparatus for the determination of the consistency of a sample of pulp.

It is a further object of the present invention to improve methods and apparatus for the determination of the consistency of a sample of pulp in the very low range of 0% to 1% and also, in the higher ranges.

It is a further object of the present invention to provide an observation station which permits a determination of the optical transmission qualities of a flowing sample of pulp.

It is a further object of the present invention to provide an observation station which permits a determination of the optical transmission qualities of a flowing sample of pulp and from the optical transmission qualities, correlating the value with known values to accurately determine the concentration of the pulp.

It is a further object of the present invention to provide an observation station for the flowing pulp which is of low resolution to thereby permit the flowing mixture of pulp to take on an artificial optical homogeneity which assists in an accurate determination of the concentration of the pulp.

It is a further object of the present invention to provide an observation station for the flowing pulp which is of low resolution due to the selection of a fairly large viewing area and the rapid flow characteristics of the pulp to thereby permit the flowing mixture of pulp to take on an artificial optical homogeneity which assists in an accurate determination of the concentration of the pulp.

It is a further object of the present invention to provide a cell for optically observing the flowing pulp and from its transmission ability, deriving an electrical output signal which is then balanced against a reference to thereby accurately determine the concentration of the pulp.

It is a further object of the present invention to provide a cell for optically observing the flowing pulp and to determine the transmission ability of the pulp by sensing the amount of light received by a detector from a source positioned opposite the sample and then translating the output of the detector into a value related to the concentration of the pulp.

It is a still further object of the present invention to provide a cell which includes a cylindrical lens for optically observing the flowing pulp and to determine the transmission ability of the pulp by sensing the amount of light received by a detector from a source positioned opposite the sample but within and not at the focal point of the cylindrical lens and then translating the output of the detector into a value related to the concentration of the pulp.

These and other objects of the present invention are directed toward establishing a means for accurately determining consistencies of pulp emanating from a headbox in the range of to 1% using photoelectric techniques. A successful apparatus, such as that described herein, to perform this function will allow better control of head box consistency with a resulting reduction in basis weight variation. In addition, it will allow basis weight changes to be made more smoothly.

There is positioned along the flow line of the pulp from a head box to the Fourdrinier a consistency measuring cell which is adapted to sample a portion of the pulp flowing therealong. The measuring cell comprises a support means in which there is positioned a glass tube through which the sample passes. Positioned within the support means is a light source which directs its energy through the sample and to a photoelectric device positioned on the opposite side of the sample from the light source. A second photoelectric detector, for maintaining a reference, is positioned juxtaposed the light source. The electrical output of the measuring photoelectric cell varies according to the consistency of the pulp. For very low consistencies, a greater output is derived from the photoelectric cell than for higher consistencies. The sampling or measuring photoelectric cell is in circuit with the reference cell in a bridge arrangement. The unbalance of the bridge is indicative of the consistency of the pulp. By comparing the magnitude of the unbalance of the bridge with the magnitude of the bridge when measuring known samples, the consistency of the unknown sample may be readily ascertained. Recording means are provided to permit a continuous record of the output of the bridge.

Greater accuracies in the measurement of the consistency of the pulp are obtained through the use of a low resolution system. The low resolution system is achieved by selecting a fairly large viewing area and at the same time passing the pulp rapidly by this viewing area so that an artificial optical homogeneity is built into the pulp. In addition, the photoelectric detector employed to measure the unknown consistency, is positioned very close to or against the transparent tube through which the pulp is flowing so that the measurement is taken at a position between the lens (the cylindrical transparent tube) and the focal point of the lens. The role that the pulp fibers play is to reflect, retract, and absorb the energy from the light source. The degree of reflection, refraction, and absorption is directly related to the amount of pulp present. One ray of light may be refracted from one fiber, only to be reflected from another, to be finally absorbed into a third fiber. Statistically, some rays of energy from the light source will pass through to the photoelectric detector.

If consistencies of pulp in higher ranges are to be measured, then the sample is diluted prior to measuring. This step places the consistency in the range where the system displays its greatest accuracy. The true consistency,

of the pulp in the stock tank or head box is then determined through the use of a dilution factor along with the output of the bridge circuit.

The invention both as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following specification taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a block diagram of the system;

FIGURE 2 is a front elevation view of the consistency measuring cell of the FIGURE 1;

FIGURE 3 is a sectional view of the consistency measuring cell taken along the line 33 of the FIG- URE 2;

FIGURE 4 is a sectional view of the consistency measuring cell taken along the line 44 of the FIGURE 3;

FIGURE 5 is an electrical schematic view of the measuring circuit of the FIGURE 1 and with the recorder shown in block form;

FIGURE 6 is a sectional view of the transparent tube through which the pulp passes and showing the relative positions of the light source and the photo-tube; and,

FIGURE 7 is a block diagram of the apparatus for diluting the pulp of higher consistency for measurement by the consistency measuring cell.

With reference to the FIGURE 1, a head box 10 supports the pulp slurry having a consistency not exceeding approximately 1%. The pulp is supplied to the head box 10 via a conduit 12, known as the stock line, from a stock tank, not shown in the FIGURE 1. The pulp is removed from the head box 10 by a pump 14 and a valve 16 is positioned between the head box 10 and the pump 14. The pump 14 supplies the pulp to a consistency measuring cell 20 via a conduit 22. A valve 24 is positioned within the conduit 22 so as to regulate the supply of pulp to the consistency measuring cell 20.

After the pulp passes through the consistency measuring cell 20 of the FIGURE 1, it may be recirculated via a valve 26 and to a conduit 28 having a valve 30 in the line. If desired, the pulp from the consistency measuring cell 20 may be recirculated back to the head box 10 via a conduit 32 which has a valve 34 interposed therebetween.

A power supply 36 supplies power to the consistency measuring cell 20, to a consistency recorder 38, and to a measuring circuit 40. The output from the consistency measuring cell is directed to the measuring circuit 40 via a conductor 42 and the output of the measuring circuit 40 is directed to the consistency recorder 38 via a conductor 44.

The FIGURE 2 is a side elevational view of the consistency measuring cell 20 of the FIGURE 1. The FIG- URE 3 is a sectional view of the measuring cell 20 taken along the line 3-3 of the FIGURE 2 and the FIGURE 4 is a sectional view taken along the line 44 of the FIGURE 3. The description of the consistency measuring cell 20 will now be made with reference to the FIG- URES 2, 3 and 4. The measuring cell 20 comprises a block 46 of rigid material such as metal, plastic, or the like which is machinable for forming the inner passageways and apertures Within the block 46. A longitudinal bore 48 is formed in the block 46 and supports a transparent cylindrical tube 50. The tube 50 is adapted to receive the pulp from the head box 10 via the conduits, valves and pumps, as shown. Means are provided for coupling the conduits into and out of the measuring cell 20 which includes a pair of connecting elements 52 and 52 having threaded bores 54 and 54 centrally disposed therein and in alignment with the central bore 48 through the block 46. The connecting elements 52 and 52' are secured to the block 46 by the studs 56, as shown.

A cylindrical aperture or recess 58 is provided in the block 46 up to the transparent tube 50 and an enlarged aperture 59 is concentric with the aperture 58 thereby providing a shoulder therebetween. There is positioned in the aperture 58, a light source 60 which is suitably mounted in the aperture 58, its mounting being in engagement with the shoulder. The light source 60 may be of the tungsten incandescent filament type. Directly opposite the aperture 58 and on the opposite side of the tube 50, is an aperture or recess 62 which houses a detector 64 which may be a photoelectric tube, or the like. An enlarged aperture 63 is concentric with the aperture 62 and forms a shoulder on which the detector 64 rests. A second detector 66 is positioned in an aperture 68 and an enlarged shoulder forming aperture 69 but at right angles to and near the aperture or recess 58 soas to receive illumination from the light source 60. In this manner, the detector 66 which may also be a photoelectric cell, serves as a reference in the bridge circuit of th FIGURE 5, to be hereinafter described.

As best shown in the FIGURE 3, the connecting elements 52 and 52 are sealed to the block 46 by a pair of O-rings 70 and 70'. In this manner, a fluid-tight seal is effected between the connecting elements 52 and 52 and the transparent tube 50.

In addition to the foregoing shouldered recesses and apertures formed in the block 46, a number of apertures are formed so as to facilitate the coupling of the electrical elements. For example, the electrical conductors, not shown, from the detector 64 may be directed through an aperture 72 into a chamber 74. Similarly, the electrical leads, not shown, from the detector 66 may be directed through an aperture of slot 76 to the same chamber 74. In addition, a slot 78, FIGURES 2 and 4, is formd from the aperture 58 to the chamber 74 which may facilitate the coupling of the electrical leads, not shown, from the light source 60 to the power supply 36 of the FIGURE 1. Other terminals may be afi'ixed within the chamber 74 for connection to the measuring circuit 40, to be hereinafter described.

To briefly summarize the construction of the consistency measuring cell shown best in the FIGURES 2, 3 and 4, a central aperture or bore 48 is provided to receive the transparent tube 50, through which the pulp advances. Connecting elements 52 and 52 are provided on each side of the block at the junctions of the ends of the tube so as to facilitate the coupling of the conduits to the measuring cell 20. A light source is provided in a recess or aperture 58 which directs its energy through the transparent tube 50 to a measuring detector or photocell 64 and also to a reference detector or photocell 66, which is positioned adjacent the light source 60. Electrical outputs are produced to components as shown in the FIGURE 5.

The electrical circuitry shown in the FIGURE 5 is a conventional bridge which includes the detector or measuring cell 64, the detector or reference cell 66, a current limiting resistor 80 and a Zero adjust potentiometer 82. The inputs to the recorder 38 are coupled by a conductor 44 from the junction of the resistor 80 and the potentiometer 82 and a second conductor 44 from the junction of the cells 64 and 66. A source of potential 84 has its negative terminal connected to the junction of the resistor 80 and the reference cell 66 by a conductor 86 and its positive terminal through a voltage limiting potentiometer 114 and then to the junction of the measuring cell 64 and the potentiometer 82 by a conductor 90. The operation of the circuitry of the FIGURE 5 will be discussed in detail durirg a discussion of operation of the system, but suffice it to say, that after the circuitry is balanced by passing clear water through the transparent tube 50, the unbalance caused by the flowing pulp and the reduced output from the measuring cell 64, will be directed to the recorder 38 via the conductors 44 and 44 and may thereby be interpreted as the consistency measurement.

In the FIGURE 6, an enlarged sectional view of the transparent tube 50, which may be of Pyrex, is shown with the pulp slurry flowing therethrough. This view permits a more detailed study of the optical conductivity or transmission qualities of the pulp. As a slurry of pulp is not a solution, it is not homogeneous in its light-or optical transmitting characteristics. By selecting a fairly large viewing area, and at the same time passing the pulp slurry rapidly by this viewing area, an artificial optical homogeneity is built into the pulp slurry. The transparent tube 50 acts as a double convex cylindrical lens or, perhaps more specifically, a first concavo-convex lens facing a second concavo-convex lens but reversed and joined by the sections of glass along the side of the tube 50 not concerned with transmitting or retracting the optical energy.

By observation from the FIGURE 6, it will be noted that the light source 60 is positioned a distance away from the tube or cylindrical lens 50 whereas the photo tube 64 is positioned adjacent the tube 50. Further, it

will be noted that the focal point of the lens formed by the tube 50 is beyond the photo-tube 64. In this manner, and by selecting a fairly large viewing area, a low resolution system is provided which compensates for the fact that the pulp being inspected, is not homogeneous. It will be noted that the tube or lens 50 refracts the optical energy and directs its rays toward the focal point. Since the liquid transporting the pulp is substantially water, little or no refraction of the optical energy takes place within the sampling area except for those rays which strike some of the pulp. The pulp may refract, reflect, or even absorb the optical energy. Statistically, some of the rays of optical energy will pass through to the photo-tube 64 to produce an output which may be interpreted as the consistency of the pulp slurry.

In the particular embodiment of the invention which was constructed and successfully operated, the transparent tube 50 was of Pyrex and had an outside diameter of of an inch and an inside diameter of of an inch. The diameter of the viewing area is controlled by the diameter of the photo-tube 64 which is 0.323 inch and in converting the inside diameter of the tube 50 to its decimal equivalent, it is 0.3725 inch. On a diameter basis, approximately 86% of the sample area is viewed and the light quantity from this area is measured as an entity.

The FIGURE 7 discloses a means whereby the consistency of pulp in excess of from 1% to 2% may be measured. The greatest accuracy in the measurement of the consistency of flowing pulp is achieved by the apparatus of the present invention if the consistency is from 0% (which is really no consistency at all but would be, for example, clear water) to 1.2% or 1.5%. Accordingly, the apparatus of the FIGURE 7 is employed when measuring consistencies from 0 to 5% or to most any consis ency, and utilizes the principle of dilution in order to bring the consistency of the pulp to within the range in which the instrument for measuring the consistency exhibits its greatest accuracy. Since the amount of dilution is known, compensation may easily be made in calculating the consistency of the unknown pulp.

As shown in the FIGURE 7, a pulp stock tank 92 supports pulp and is connected to a pump 94 through the conduit as shown. The output of the pump 94 is delivered to a second pump 96 through a valve 98 and also to a conduit 100 which may be connected to a head box, another tank, etc. Dilution water at known rates of flow is delivered to a pump 102 through a valve 104 in the conduit 106. The output of the pump 96 is connected to a valve 108 while the output of the pump 102 is connected to a valve 110. The flow from the valves 108 and 110 is then connec ed to a common conduit 112 which is then directed to the consistency measuring cell 20 which is substantially identical to the cell 20 of the foregoing figures.

Before setting forth the manner of operation of the invention, a number of operating parame ers will be given. The transparent tube 50 through which the pul flows, was a Pyrex tube having an outside diameter of 42 inch and an inside diameter of of an inch. The optical focal length of the tube 50 which, of course. is the double concavo-convex lens is approximately inch. The photo-electric cell 64 is in contact with the sample tube 50 and, therefore, as shown is not at the focal point of the lens. This feature contributes to the low resolution, which is desi ed, of the system. The pulp is pumped through the tube 50 at approximately 7.4 miles per hour or 7847 inches per minute. The viewing area provided by the photo-tube 64 is approximately 0.323 inch in diameter. On a diameter basis, approximately 86% of the sample area is viewed and the light quantity or optical transmission from this area is measured as an entity. One finite cross-section of the pulp slurry will pass along the diameter of the viewing area in minute or approximately 2.47 milliseconds. The assessment of the size of a flock of the pulp slurry is not readily attainable; however, it is believed that any one flock will not remain in the viewing area an appreciable length of time to contribute a false signal. A large viewing area with respect to the area of sample is of assistance in developing low resolution and, in turn, the blurring of the image at the photoelectric cell 64.

Prior to operating the system, a number of samples of pulp of known consistencies are passed through the consistency measuring cell 20 and the electrical output of the bridge circuit of the FIGURE on the conductors 44 and 44 is recorded by the recorder 38. In this manner, the electrical output for a given consistency is determined. The consistency of an unknown sample may be determined for reference purposes by weighing a given sample, dehydrating the sample, weighing the dehydrated sample, and finally comparing the second weighing with the first weighing which yields the consistency of the unknown sample in an identifiable form. For ease in interpreting the consistency values, the recorder 38 may have its scale converted to percent consistency so that a visual observation will readily reveal the consistency of the pulp immediately flowing through the consistency measuring cell 20.

With reference to the FIGURE 1, the head box 10 is supplied with the pulp from a stock line 12 and the valves 16 and 24 are opened. We Will assume that we wish to return the sample to the head box 10 via the conduit 32 so that the valve 34 will also be opened. The pump 14 is then started and electrical power supplied to the cell 20, the recorder 38, and the measuring circuit 40 by the power supply 36. After the system has reached stability, the consistency of the pulp is then being accurately measured and recorded by the circuit of the FIGURE 5.

It will be understood that prior to measuring the con-- sistency of an unknown pulp slurry, a sample of water would be passed through the measuring cell so as to adjust a variable resistor 114 associated with the source of potential 84 and also the zero adjust potentiometer 82. Hereafter, the system operates without further attention and readily provides the pulp consistency through the output of the bridge circuit of the FIGURE 5. As shown in the FIGURE 6, the flowing pulp will reflect, refract, or absorb, or any combination of these, the optical energy from the light source 60 before permitting some of the energy to impinge upon the photo-tube 64. The unbalance of the bridge circuit of the FIGURE 5 is then electrically manifested upon the output conductors 44 and 44'.

For determining the consistency of pulp having fairly high consistencies, a known amount of dilution water would be added via the conduit 106 of the FIGURE 7 prior to measuring. With the valves 98, 104, 108 and 110 opened and the pumps 94, 96 and 102 started, a diluted mixture of pulp will be supplied via the conduit 112 to the consistency measuring cell 20. The dilution factor Will then be considered in interpreting the recorded value of the FIGURE 5. As a matter of convenience, the scale of the recorder 38 could be varied so as to directly read and interpret the consistency of the sample prior to dilution.

Thus, the present invention may be embodied in other specific forms without departing from the spirit and the essential,characteristics of the invention. The present embodiment is, therefore, to be considered in all respects as illustrative and the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are, therefore, intended to be embraced therein.

What is claimed is:

1. Apparatus for measuring the consistency of a nonhomogeneous mixture and substances of differing optical qualities comprising a cell having a channel therethrough, a hollow cylindrical lens positioned within said channel, an observation station having a first aperture along one side of said lens and opening into said channel and a second aperture on the opposite side of said lens and opening into said channel, means to supply non-homogeneous mixture at a substantially constant rate through said lens, and radiant energy means positioned within said aperture for measuring the radiant energy transmission qualities of the flowing non-homogeneous mixture, said radiant energy means including light source means within said first aperture for directing light through said lens and across the path of movement of said mixture, and light responsive means located in said second aperture for receiving a blurred image thereon and for changing the electrical properties thereof in response to said blurred image Wi.hout being substantially affected by the nonhomogeneous nature of said mixture.

2. A mixture consistency measuring apparatus comprising a cell, a circular bore through said cell, a transparent tube having refractive qualities and an optical focal point and positioned within said bore, a first aperture formed in said cell to said tube opening into said channel and having a lateral dimension transverse to said tube which is at least as great as the outside diameter of said tube, a second aperture formed in said cell to said tube and at a side opposite to said first aperture, and radiant energy detecting means positioned within said aperture for measuring the quantity of radiation passing through said tube, said radiant energy detecting means including photoelectric detector means positioned beyond said tube but removed from the focal point of said tube for receiving a blurred image thereon indicative of the consistency of the mixture.

3. Apparatus for determining the consistency of a mixture within a predetermined optimum consistency range to indicate the consistency of a mixture which is outside said range comprising a cell having a channel for the passage of a mixture therethrough; an observation station along said channel and within said cell; means for providing a mixture having the consistency outside said predetermined range including means for passing said mixture past said cell for further use; means for diluting the mixture including means for diverting a limited quantity of said mixture having a consistency outside said predetermined range from said means for passing and at a controlled predetermined rate of flow, means for supplying a diluent at a controlled predetermined rate of flow, means for bringing together said portion of said mixture from said means for diverting a limited quantity of said mixture and said diluent from said means for supplying a diluent for providing a diluted mixture and means to supply the diluted mixture to said cell at a substantially constant flow rate; and radiant energy means positioned within said observation station for measuring the radiant energy transmission qualities of the diluted mixture; whereby variations in the consistency of said mixture having a consistency outside said predetermined range is evidenced by variations in the consistency of said diluted mixture within said predetermined range.

v 4. The combination as defined in claim 3 including means in circuit with said radiant energy means for determining the consistency of the diluted mixture.

5. A low resolution measuring apparatus for determining the consistency of a non-homogeneous mixture of substances of differing optical qualities comprising a hollow cylindrical lens having refractive qualities and an optical focal point beyond the circumference of the lens, directing means for passing the non-homogeneous mixture through said hollow cylindrical lens, a light source for directing light through said lens and across the path of said mixture passing therethrough, and photo-detecting means positioned adjacent said lens at a side opposite to said light source and removed from the focal point of said lens for receiving a blurred image indicative of the consistency of the mixture in transit therepast, whereby said photo-detecting means is less sensitive to the non homogeneous nature of said mixture and more responsive to the consistency of the over-all mixture.

6. The apparatus according to claim 5 wherein said light source is mounted proximate said lens for illuminating a major portion of the cross sectional area of the interior of said lens to provide a relatively large illuminated sample of the mixture in said lens, said photodetecting means being located to receive substantially all the light passing through said lens.

7. The apparatus according to claim 5 including means electrically connected with said photo-detecting means for producing a low-resolution electrical signal representative of the blurred image produced upon said photodetecting means, whereby said electrical signal represents the consistency of the over-all mixture substantially unafiected by the non-homogeneous nature of said mixture.

8. Apparatus for measuring the consistency of a nonhomogeneous mixture of substances of dilfering optical qualities including means for passing a portion of the mixture along a predetermined path, light source means located to one side of said path for directing light through a portion of said path, photo-detecting means located adjacent said path for receiving light from said light source means passing through said path and lens means intermediate said light source means and said photodetecing means for producing a low-resolution blurred image indicative of the consistency of the mixture in transit along said path, said lens means having a predetermined focal length at which a substantially high resolution clear image would be produced and said photodetecting means being located from said lens means a distance other than said focal length for receiving said low-resolution blurred image.

9. Apparatus according to claim 8 wherein said means for passing includes means for impelling said portion of the mixture at a rate of speed sufficient to efiect a further reduction in the resolution of the response of said photodetecting means.

10. The apparatus according to claim 9 wherein said light source means directs light through a portion of said path which is relatively large with respect to individual particles and groups of particles of one of said substances for reception by said photo-detecting means to substantially preclude a response by said photo-detecting means to individual particles and groups of particles passing along said path.

References Cited UNITED STATES PATENTS 1,794,222 2/1931 Whitney. 3,028,501 4/ 1962 Lamparter. 3,358,148 12/1967 Conklin et a1.

OTHER REFERENCES Colorimetry by Albert A Shurkus Radio News, June 1944, pages 25 and 26, relied upon.

RONALD L. WIBERT, Primary Examiner V. P. MCGRAW, Assistant Examiner US. Cl. X.R. 

